The CRAY-2 hardware was constructed of synchronous networks of binary circuits. These circuits were packaged in 320 pluggable modules. The modules each contained 750 integrated circuit packages. The total integrated circuit population in the system was 240,000 units of which 75,000 were the memory.

The pluggable modules were three-dimensional structures with an array of circuit packages 8 by 8 by 12 units. There were eight printed circuit boards which formed the module structure. Circuit interconnections were made in all three directions within the module. External dimensions of the module were one inch by four inches by eight inches. One end of the module contained a circuit connector which mated with a connector in the cabinet frame. This connector had 288 pairs of pins for twisted pair wire communications between the modules in the cabinet frame.

Modules were arranged in the cabinet frame in 14 columns each 24 modules height. The columns were arranged in a portion of a circle with a 20-degree angle between columns. An inert electronic liquid circulated in the cabinet frame and flowed through the module circuit boards across the four-inch surface. Liquid velocity was one inch per second through the modules. Total module column height was 24 inches.

The semicircle of module columns was located on top of a similar structure containing power supplies for the system. Total power consumption for the system was 180 kilowatts. Total cabinet height including the power supplies was 43 inches.

There were 20 types of integrated circuit packages used in the logical networks of the machine. The circuits consisted of emitter coupled logic gates with a maximum gate width of six inputs. Total gate capacity of the circuit packages was 16. Most of the 20 types of circuit packages contained two levels of gates within the package. The package had 16 connecting pins.

A 250 megahertz oscillator controlled the timing throughout the circuit modules in the machine. The oscillator signal was transmitted as a square wave over 120 ohm twisted pair wires to each of the module connectors. Wire lengths were controlled so that the travel time to the individual modules was accurate to within 100 picoseconds. The oscillator square wave was delivered to each individual circuit package within the module. An 800 picosecond pulse was formed from the square wave to gate data into register latches within the packages. This 800 picosecond strobe pulse occured simultaneously throughout the machine with a period of 4 nanoseconds. This time was referred to as the machine clock period.

Circuit Board ConstructionEach circuit board was four inches wide and eight inches long. Each board had six layers. The two outside layers, referred to as the vertical and horizontal layers due to the orientation of their foil runs, carried logic signals between the integrated circuits on the board. Logic signals between the back-panel connector and the gate array chips also used these two foil layers. The inner board layers were used to distribute power, system clock, and ground to each chip location. There were two power layers, -5.2 volts and -2.0 volts, one system clock layer, and one ground layer. The system clock layer was used, on a very limited basis.

Circuit Board Power and Ground ConnectionsAt one end of each printed circuit board the power and ground foil layers were connected to foil pad areas on the top and bottom surfaces of the board. The power and ground bus lead connection blocks were inserted between the boards at the pad areas when the eight boards are assembled to make a complete module. The power bus blocks served a dual purpose in the module as spacers between boards and as power bus connections. Each module had seven power bus leads to be connected to the -5.2v system bus bar, seven for the -2.0 power, and fourteen ground leads.

Circuit Board Input/Output Signal ConnectionsAt the end of the circuit board opposite the power connections, a 72 pin connector was mounted serving as both an input/output signal connector and as a board spacer when the module was assembled. This connector was divided into three sections of 24 pins each, with the three sections being assigned the same letter designations as the chip fields of the board on which they were mounted, as described in the "The CRAY-2 Module" post. The 24 pins in each section were labeled (A through X). This allowed reference to any one of the 576 pins on the module using a simple two letter designator, the first being the connector section and the second indicating the pin within the section.

Note: This data has never been published publicly, please credit when posting.